The optional criteria for the tennis racket is to maximize the performance while minimizing the risk of injury.
In general, tennis rackets employ a frame with strings, or a frame, a head, a handle, and strings. Such construction of the tennis racket affects the load to the hand, the arm, and the shoulder of the tennis player. The loads by the incoming tennis ball on the tennis racket results—vibration, shock, and twisting
These loads are determinates of the risk for injury.
The vibrations result from the strings and from the oscillation of the racket frame. These types of oscillations create an adequate level of resulting energy and require the muscle activation to withhold such reaction. The frame structure has influence on the amplitude of the vibration. Therefore, gripping the handle tighter decreases the oscillation of the energy, but transforms the energy to the forearm muscles and results in lessening the risk of injury.
When the tennis ball strikes the tennis racket, a shock develops that causes a reaction in the hand and the arm to the shock. To withstand and remove shock energy, the muscles have to be activated and act as the shock absorber. This reaction results in lessening of the risk of injury.
Another reaction is when the tennis ball strikes the center of the tennis racket, and this results in a twisting torque. The muscles react to control this condition and therefore result in lessening the risk of the wrist to injury.